Survival of shoot meristems of tomato seedlings frozen in liquid nitrogen

An explant containing the primary shoot meristem was dissected from intact tomato seedlings after thawing from liquid nitrogen. Surviving explants produced shoots directly by normal meristem growth when cultured in the presence of gibberellic acid. Without gibberellic acid all surviving explants produced callus tissue and subsequently adventitious shoots, with no direct outgrowth of the primary meristem.Dimethyl sulphoxide (15%) in culture medium and a cooling rate changing continuously from 20 to 55 °C min^?1 between 0 and ?120 °C were required for optimal survival.Nonfrozen material produced shoots directly without the requirement for gibberellic acid indicating that hormonal regulation of organised growth by the shoot meristem had been altered by the freeze/ thaw process.